1. Field of the Invention
This invention relates to the passivating of scaling species in water.
2. Description of Related Art
Water chemistry dominates and limits the design of desalination processes. Most separations are limited by precipitation of slightly soluble compounds such as CaCO3 or CaSO4 rather than by inherent physical characteristics such as osmotic pressure. For example, in desalination of inland brackish water sources, reverse osmosis is typically limited to around 75% water recovery by the presence of small amounts of scaling species such as Ca2+, SO42−, and HCO3−, while osmotic pressure alone would impose a much higher limit of 98% recovery if only Na+ and Cl− were present. The consequences of low water recovery are 1) larger pumps, intakes, outfalls, and pretreatment systems, and 2) larger volumes of reject streams associated with lost water. The first consequence plays out most clearly in thermal desalination of seawater, where most processes run at only 25-35% water recovery and sub-optimum temperature due to scaling species. The second consequence seriously impacts the viability of inland desalination of brackish water.
Accordingly, a need exists for an effective solution to reduce the concentration of scaling species in the desalination process.